The present invention relates to industrial ovens used for heating objects involved in processes such as fabrication processes and, more particularly, to ovens for heating such objects in compartments while motionless.
There are many operations in fabrication processes that require heating of the product being fabricated or the heating of some intermediate structure or portion that will be in or involved in the final product. Some common heating operations in processes for fabricating electronic devices include solder reflowing operations in which solder, provided as a paste on printed circuit board (PCB) assemblies between terminals of circuit-components to be mounted on the board and conductive interconnections provided on the board, is melted to form electrical connections therebetween, curing operations to complete the bonding and solidification of adhesives and fills used in mounting components and the like, and ball bonding operations to attach solder spheres formed on circuit components to ball grid array structures.
Currently, in-line mass reflow ovens-dominate as the heating device for such operations such as that shown in U.S. Pat. No. 5,440,101 hereby incorporated herein by reference. Ovens of this type melt the solder paste by transporting PCBs with the paste and circuit components thereon through multiple, consecutive heating zones in the ovens of differing temperatures to thereby apply heat at differing rates to the PCBs and components. Such ovens transfer heat to the PCBs and components via radiant dominant heating, convection dominant heating, or a combination of both, in either an air atmosphere or, alternatively, an inert atmosphere to thereby control the degree of resulting oxidation of the PCBs and the circuit components thereon. To integrate the oven in the production line, the PCBs with components are passed via a conveyor arrangement into the oven in which the solder paste thereon is melted, and thereafter further pass the PCBs with the components now soldered thereon to further downstream process operations. Since the specified heating profile (temperature as a function of time) recommended for melting the solder has not changed significantly over the last decade, the increases that have occurred in that time in product throughput in upstream process operations have also lead to longer and longer ovens to thereby provide enough capacity to deal with the resulting faster conveyor speeds.
To reduce the concomitant need for more floor space, oven manufacturers have previously tried two approaches: 1) multi-lane ovens with special shuttle conveyors (based on the theory that a two lane highway can move more cars than a single lane); and 2) elevators inside vertical process chambers. However, such vertical process chambers were unable to adequately control the resulting heating profile occurring therein because the convection flow of the heating fluid did not directly impinge on each board in the same manner and it was too difficult to overcome the natural vertical convection flow, i.e. xe2x80x9cheat rises.xe2x80x9d Thus, there is a desire for an oven taking relatively little floor space which has the capacity to accommodate rapid influxes of PCBs with circuit components thereon provided thereto in a production line and subject them to relatively precise temperature profiles during the heating and cooling thereof before passing them on to the remaining portions of the production line, and do so at a reasonable cost.
The present invention provides an oven compartment in an oven for subjecting items to a selected heating sequence having a compartment container with a transport opening therein to permit selectively entering such items into portions of container interior regions and with a first heat flow opening therein to permit forcing a heating fluid into a first plenum structure located in the interior regions of the compartment container. The first plenum structure has a perforated surface next to which an entered item from the transport opening can be positioned with there being a first heating duct extending between the first heat flow opening and the first plenum structure to allow providing heating fluid at locations near the perforated surface. The first plenum structure has a material mass and a specific heat such that a rate of change of temperature of that structure exceeds one degree Centigrade per second for a selected maximum temperature differential between heating fluid and any entered items positioned adjacent to the perforated surface at selected heating fluid pressures at that perforated surface.
A method for heating such items entered into the compartment container next to the perforated surface of the first plenum structure with a heating fluid previously heated by a heater, to an extent determined by operating a heater control, directed onto such items is based on obtaining a control representation of a selected set of values for the heater control versus time over a selected heating duration based on a heating specification for a selected kind of item to be heated. Heating fluid is directed over the heating duration onto such an item with this heating fluid having been previously heated by the heater through operating the heater control to follow the control representation as selectively further adjusted based on measurements of heating fluid near the perforated surface performed in the heating duration.